I came across the problem that when using something like:
to_char(my_datefield,'D') as dow
to find out the date, this might behave differently on the pentaho production-server, the report designer and (if applicable) an underlying PDI transformation. When connecting to the Oracle-Server, you can click on “advanced” and set the locale to what you need – for example
ALTER SESSION SET NLS_TERRITORY = BELGIUM;
That way, your transformation/report will behave consistently across servers/environment.